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O. J. P. Eboli

Publications and source records attributed to O. J. P. Eboli.

89 records · Page 5Linked to original sources
arXiv1996

Constraints on Quartic Vector-Boson Interactions from Z Physics

We obtain the constraints on possible anomalous quartic vector-boson vertices arising from the precision measurements at the $Z$ pole. In the framework of $SU(2)_L \otimes U(1)_Y$ chiral Lagrangians, we examine all effective operators of order $D=4$ that lead to four-gauge-boson interactions but do not induce anomalous trilinear vertices. We constrain the anomalous quartic interactions by evaluating their one-loop corrections to the $Z$ pole physics. Our analysis is performed in a generic $R_ξ$ gauge and it shows that only the operators that break the $SU(2)_C$ custodial symmetry get limits close to the theoretical expectations. Our results also indicate that these anomalous couplings are already out of reach of the Next Linear $e^+ e^-$ Collider, while the Large Hadron Collider could be able to further extend the bounds on some of these couplings.

hep-ph↗
arXiv1996

Higgs Physics at LEP2

In this report we review the prospects for Higgs physics at LEP2. The theoretical aspects and the phenomenology of Higgs particles are discussed within the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM). The experimental search techniques are described and the discovery limits for Higgs bosons in the LEP2 energy range are summarized. In addition, opportunities of detecting Higgs particles in non-minimal extensions of the SM and the MSSM are investigated.

hep-ph↗
arXiv1995

Quantum evolution of scalar fields in Robertson-Walker space-time

We study the $λϕ^4$ field theory in a flat Robertson-Walker space-time using the functional Schödinger picture. We introduce a simple Gaussian approximation to analyze the time evolution of pure states and we establish the renormalizability of the approximation. We also show that the energy-momentum tensor in this approximation is finite once we consider the usual mass and coupling constant renormalizations.

hep-th↗
arXiv1995

Excited Leptonic States in Polarized e^-γand e^+ e^- Collisions

We analyze the capability of the next generation of linear electron--positron colliders to unravel the spin and couplings of excited leptons predicted by composite models. Assuming that these machines will be able to operate both in the $e^+e^-$ and $e^-γ$ modes, we study the effects of the excited electrons of spin $\frac{1}{2}$ and $\frac{3}{2}$ in the reactions $e^-γ\rightarrow e^-γ$ and $e^+e^- \rightarrow γγ$. We show how the use of polarized beams is able not only to increase the reach of these machines, but also to determine the spin and couplings of the excited states.

hep-ph↗
arXiv1995

Anomalous g^5_z coupling at $γγ$ colliders

We study the constraints on the anomalous coupling $g^Z_5$ that can be obtained from the analysis of the reaction $γγ\rightarrow W^+ W^- Z$ at future linear $e^+e^-$ colliders. We find out that a $0.5$ ($1$) TeV $e^+e^-$ collider operating in the $γγ$ mode can probe values of $g_5^Z$ of the order of $0.15$ ($4.5 \times 10^{-2}$) for an integrated luminosity of $10$ fb$^{-1}$. This shows that the ability to search for this anomalous interaction of the $γγ$ mode is better than the one of the usual $e^+e^-$ mode, and it is similar to the ability of the $eγ$ mode.

hep-ph↗
arXiv1995

Quartic Anomalous Couplings in $γγ$ Colliders

We study the constraints on the vertices $W^+W^- Zγ$, $W^+W^-γγ$, and $ZZγγ$ that can be obtained from triple-gauge-boson production at the next generation of linear $e^+e^-$ colliders operating in the $γγ$ mode. We analyze the processes $γγ\to W^+W^-V$ ($V=Z$, or $γ$) and show that these reactions increase the potential of $e^+e^-$ machines to search for anomalous four-gauge-boson interactions.

hep-ph↗
arXiv1994

Bounds on Scalar Leptoquarks from Z Physics

We analyse the constraints on scalar leptoquarks coming from radiative corrections to $Z$ physics. We perform a global fitting to the LEP data including the contributions of the most general effective Lagrangian for scalar leptoquarks, which exhibits the $SU(2)_L \times U(1)_Y$ gauge invariance. We show that the bounds on leptoquarks that couple to the top quark are much stronger than the ones obtained from low energy experiments.

hep-ph↗
arXiv1994

$ε_b$ Constraints on Self--Couplings of Vector Bosons

We analyze the constraints on possible anomalous contributions to the $W^+W^-Z$ vertex coming from non-universal radiative corrections to the $Z \rightarrow b \bar{b}$ width. We parametrize these corrections in terms of $ε_b$ and use the LEP data to establish the allowed values for the anomalous triple couplings. We examine all CP conserving effective operators that exhibit $SU(2)_L\times U(1)_Y$ gauge invariance and do not give any tree level contribution to the present experimental observables. For some of these operators our constraints are comparable with the bounds coming from a global fit of the oblique parameters, which evidences the increasing relevance of the precise measurement of the $b$--quark parameters at LEP for the search of new physics.

hep-ph↗
arXiv1993

Searching for an Invisibly Decaying Higgs Boson in E^+E^-, E-Gamma, and Gamma-Gamma Collisions

Higgs bosons can have a substantial ``invisible'' branching ratio in many extensions of the Standard Model, such as models where the Higgs bosons decay predominantly into light or massless weakly interacting Goldstone bosons. In this work, we examine the production mechanisms and backgrounds for invisibly decaying Higgs bosons at the Next Linear $e^+e^-$ Collider operating in the modes $e^+e^-$, $eγ$, and $γγ$. We demonstrate that such machine is much more efficient to survey for invisibly decaying Higgs bosons than the Large Hadron Collider at CERN.

hep-ph↗
arXiv1993

Signals for Vector Leptoquarks in Hadronic Collisions

We analyze systematically the signatures of vector leptoquarks in hadronic collisions. We examine their single and pair productions, as well as their effects on the production of lepton pairs. Our results indicate that a machine like the CERN Large Hadron Collider (LHC) will be able to unravel the existence of vector leptoquarks with masses up to the range of $2$--$3$ TeV.

hep-ph↗
arXiv1993

Triple Vector Boson Processes in $γγ$ Colliders

We study the production of three gauge bosons at the next generation of linear $e^+e^-$ colliders operating in the $γγ$ mode. The processes $γγ\rightarrow W^+W^-V$ ($V=Z^0$, or $γ$) can provide direct information about the quartic gauge-boson couplings. We analyze the total cross section as well as several dynamical distributions of the final state particles including the effect of kinematical cuts. We find out that a linear $e^+e^-$ machine operating in the $γγ$ mode will produce 5--10 times more three-gauge-boson states compared to the standard $e^+e^-$ mode at high energies.

hep-ph↗
arXiv1993

Quartic Anomalous Couplings in $eγ$ Colliders

We study the production of gauge boson pairs at the next generation of linear $e^+e^-$ colliders operating in the $eγ$ mode. The processes $eγ\rightarrow VV^\prime F$ ($V,V^\prime =W$, $Z$, or $γ$ and $F=e$ or $ν$) can give valuable information on possible deviations of the quartic vector boson couplings from the Standard Model predictions. We establish the range of the new couplings that can be explored in these colliders based on a $3σ$ effect in the total cross section. We also present several kinematical distributions of the final state particles that could manifest the underlying new dynamics. Our results show that an $eγ$ collider can extend considerably the bounds on anomalous interactions coming from oblique radiative corrections and from direct searches in $e^+e^-$ colliders.

hep-ph↗
arXiv1993

Searching for Leptoquarks in electron-photon Collisions

We study the production of composite scalar leptoquarks in $eγ$ colliders, and we show that an $e^+e^-$ machine operating in its $eγ$ mode is the best way to look for these particles in $e^+e^-$ collisions, due to the hadronic content of the photon.

hep-ph↗
arXiv1993

Identifying the Higgs Boson in Electron--Photon Collisions

We analyze the production and detection of the Higgs boson in the next generation of linear $e^+e^-$ colliders operating in the $eγ$ mode. In particular, we study the production mechanism $e + γ\rightarrow e γγ\rightarrow e + H$, where one photon is generated via the laser backscattering mechanism, while the other is radiated via the usual bremsstrahlung process. We show that this is the most important mechanism for Higgs boson production in a $500$ GeV $eγ$ collider for $M_H\raisebox{-.4ex}{\rlap{$\sim$}} \raisebox{.4ex}{$>$}140$ GeV. We also study the signals and backgrounds for detection of the Higgs in the different decay channels, $b \bar b$, $W^+W^-$, and $ZZ$, and suggest kinematical cuts to improve the signature of an intermediate mass Higgs boson.

hep-ph↗
arXiv1993

Measuring the Gamma-Gamma Coupling of the Higgs at Linear Colliders

Observing the production of the Higgs particle in the $γ$-$γ$ mode of a linear $e^+e^-$ collider allows for the measurement of the $Hγγ$ coupling. We point out that for the intermediate Higgs mass range this measurement is considerably more challenging than previously believed. The $b \bar b$ signature receives a large background from the production of heavy quark pairs by resolved photons. We quantify the experimental requirements needed to make a meaningful measurement in the presence of this background.

hep-ph↗
arXiv1992

Threshold Effects on Heavy Quark Production in $γγ$ Interactions

The exchange of gluons between heavy quarks produced in $e^+e^-$ interactions results in an enhancement of their production near threshold. We study QCD threshold effects in $γγ$ collisions. The results are relevant to heavy quark production by beamstrahlung and laser back-scattering in future linear collider experiments. Detailed predictions for top, bottom and charm production are presented.

hep-ph↗